Freeze drying apparatus and method



April 6, 1965 M. E. FUENTEVILLA FREEZE DRYING APPARATUS AND METHOD FiledJuly 24, 1961 r I a 3 Sheets-Sheet l FIG.|

\LOAD CELL'S L ll:

INVENTOR. MANUEL E. FUENTEVILLA BY MAW ATTORNEY April 9 M. E.FUENTEVILLA 3,176,408

FREEZE DRYING APPARATUS AND METHOD Filed July 24, 1961 3 Sheets-Sheet 25 llNERT GAS INVENTOR. MANUEL E. FUENTEVILLA MHM ATTORNEY April 5 M. E.FUENTEVILLA 3,176,408

FREEZE DRYING APPARATUS AND METHOD Filed July 24, 1961 3 Sheets-Sheet 3INVENTOR. MANUEL E. FUENTEVILLA By Mww ATTORNEY "United States PatentOfiice 3,176,4h8 Patented Apr. 6, 1965 3,176,408 FREEZE DRYING APPARATUSAND METHOD Manuel E. Fuentevilla, Haddonfield, N..l., assignor, by mesneassignments, to Pennsalt Chemicals Corporation, Philadelphia, Pa., acorporation of Pennsylvania Filed July 24, 1961, Ser. No. 126,234Claims. (Cl. 34-5) This invention relates to a freeze drying apparatusand method, and more particularly to a freeze drying apparatus andmethod wherein the freeze drying cycle is automatically controlled inresponse to the loss of weight of the articles undergoing freeze drying.

Numerous processes and apparatus for freeze drying specimens have been,proposed heretofore. In such devices and processes proposed heretofore,the length of the freeze drying cycle is based on empirical formulae.Accordingly, the cycle for the freeze drying process is nothing morethan a calculated guess. Accordingly, it will be obvious that numerousinefficiencies are present in the apparatus and methods proposedheretofore.

The, present invention is directed to a method and apparatus wherein thefreeze drying cycle is automatically controlled in response to the lossof weight of the articles being freeze dried. When using the apparatusor method of the present invention, it is not necessary for an operatorto set any controls as to the timing of the cycle nor periodicallyinspect the articles being freeze dried so as to ascertain the status ofthe articles. In accordance with thepresent invention, the loss ofweight of the articles being freeze dried is ascertained in accordancewith any one of the embodiments of the present invention and means areprovided for automatically stopping or varying the freeze drying cyclewhile at the same time activating an alarm so as to alert the operator.

In accordance with the present invention, the change in the loss ofweight of the articles being freeze dried is ascertained in response toload cells which supportthe articles or in response to the electricalresistivity of the articles. As a result of the change in the weight ofthe articles being freeze dried, the heat being supplied to the articlesmay be, varied, or the pressure within the chamber enclosing thearticles may be varied.

' It is an object of the present invention to provide a novel apparatusfor freeze drying articles.

"It is another object of the present invention to provide a novel methodfor freeze drying articles.

It is still another object of the present invention to provide a novelapparatus for freeze drying articles wherein the freeze drying cycle isautomatically controlled in response to the change in weight of thearticles being freeze dried.

It is a still further object of the present invention to provide a novelmethod of freeze drying articles by varying the freeze drying cycle inresponse to the change of weight in the articles being freeze dried.

Other objects will appear hereinafter.

For the purpose of illustrating the invention there is shown in thedrawings forms which are presently preferred; it being understood,however, that this invention is not limited to the precise arrangementsand instrumentalities shown.

FIGURE 1 is a schematic illustration of freeze drying apparatus inaccordance with the present invention.

FIGURE 2 is a schematic illustration of another embodiment of thepresent invention.

FIGURE 3 is a schematic illustration of another embodiment of thepresent invention.

FIGURE 4 is a schematic illustration of another embodiment of thepresent invention.

FIGURE 5 is a schematic illustration of another embodiment of thepresent invention.

Referring to the drawing in detail, wherein like numerals indicate likeelements, there is shown in FIGURE 1 a freeze drying apparatusdesignated generally as 10.

The freeze drying apparatus illustrated schematically as 10 comprises ahousingv 12 having a plurality of hollow shelves 14 disposed one abovethe other and supported by said housing. Only one such shelf isillustrated in the drawing. The shelf 14 is hollow so that a heatingmedium may be circulated therethrough. The interior of the shelf 14 isconnected to an inlet conduit 16 and an outlet conduit 18.

The conduits 16 and 18 are connected to a pump 20 which continuouslycirculates the medium through the shelf 14. A heat exchanger 22 isdisposed in the conduit 16 between the pump 20 and the shelf 14. Thetemperature of the heat exchanger 22 is regulated by a controlling fluidsuch as steam which is circulated therethrough by means of the inletconduit 24 and the outlet conduit 26. The outlet conduit 26 is connectedto a steam generator 28 having a pump 30. The outlet side of the pump 30is connected to the inlet conduit 24. A valve 32 having a solenoidoperator 34 is disposed within the conduit 24.

The shelf 14 is supported by load cells 36 and 38. Load cells 36 and 38are commercially available devices which generate an electric current inresponse to pressure. Such load cells are extremely accurate and are noteffected by the temperatures and pressures within the housing 12. Theload cells 36 and 38 are connected to the weight recorder and controller44 by wires 46 and 42. The weight recorder and controller 44 is acommercially available device which permanently records the electricalcurrent generated by the load cells 36. and 38 on a graph which may beinterpreted in terms of weight. In addition, the weight recorder andcontroller 44 relays the current received from the load cells 36 and 38to a controller 46.

The controller 46 regulates the flow of motive fluid to the diaphragm ona valve 48 in the conduit 50. The conduit 5%) is connected to theinterior of the housing 12. The conduit 50 is provided with a vacuumpump 52 for evacuating the interior of the housing 12. An alarm 54 isconnected to the weight controller and recorder 4,4 and is responsive toa minimal amount of current.

A tray is supported by the shelf 14 with legs on said tray spacing thesame from the shelf 14. The tray 60 is filled with articles 62 which areto be freeze dried within the housing 12. The, condenser 66 is connectedto the housing 12 by means of a conduit 64'.

The apparatus 10 operates as follows:

A tray 66 of articles 62; which are to be, freeze dried is disposedwithin the housing 12 On the shelf; 14;. The articles 62 are prefrozen.The door (not shown) providing access to the interior of the housing; 12is provided with a seal means to that the housing 12 is hermeticallysealed in the closed disposition of the door. A heating fluid iscirculated through the shelf 14. by means of conduits 16 and 18. Thecirculating fluid within the shelf 14 beats the articles 62 byradiation. All surfaces are colored black while the inner'gsurfaceon'the doorf is colored white.

As the articles 62 are heated by radiation, they are V 5 closes aplurality of'embodiments capable of controlling subject to a vacuumwithin the housing 12 effected by the pump 52. The combination of heatand the vacuum causes the ice within the frozen articles 62 to sublimewith the resultant vapor being removed by therpurnp 52; As the iceWithin the articles oz sublimes, the weight 1Q trated. For example, itis often'desirable to connect supported by the load cells 36 and 38decreases. 7

After a predetermined period of time,-the weight of the articles 62 willbecome stabilized thereby indicating" that substantially allroftheice isremoved therefrom by sub-,

limation. a v

During the entire cycle, the controllen44ris recording the change in thecurrent generated by the load cells 36' and 38 and relaying the same toalarm 54 and controller 45. a In response to a minimum currentindicating that'- substantially all ice has been removed fromthearticles '62, the alarm 54 is activated and controller46 is activatedso as to close the valve 48. Thus, it will be seen that the freezedrying cycle is controlled so as to stop v V the cycle as soon assubstantially allof theice has been removed from the'articles 62. v V nIt has been determined that there is an optimum rate of change of weightof the articles 62 with respect to I time. It is possible to utilize acontroller 46 which is of it the type which is capable .of receiving asignal" from the controller 44' so that the valve'48 is constantlyvaried durf ing the freeze drying process. Thus, the apparatus 1 may beoperated with optimum efiiciency; I 1 An alternative embodiment of thepresent invention is illustrated schematically in FIGURE 2 anddesignated generally as 90. S Thetapparatus 9% is substantiallyidentidal with the apparatus except as will be madeclear hereinaften'The controller 44 relays ja signalto a solef noid 7tl which operates thevalve 63'in the conduitot). V In response to a minimalsignal, thesolenoid '70 is .ac-

tuated to regulate the valve 68. The outlet side of the f condenser 66is connected to manner side. of the vacuum" pump so that all condensateis removed fromthe air by g the condenserfdo beforebeing dischargedtoratmosphere by the pumpconnected thereto;

There is shown in FIGURE another embodiment of the present inventiondesignated generally. as; 91. .The apparatus 91 is substantiallyidentical with the apparatus 10 except as Willbe made clear hereinafter.In the lapfparatus 91, the signal received -,by theweightrecordercontrol is transmitted to the controller :46 Which'controls Y the how ofmotive fluid to the diaphragm actuated valve: 58 in the conduit 56. 1The conduit 56' is'utilized to injecu .an inert atmo'sphere'into thehousing 12. The injection;

of an inert atmosphere inthe housing lz' slowsidown' the freeze dryingcycle .sinceit effects the vacuum therein.

As shown more clearly in FIGURE 4,-anotherfem bodiment of the presentinventiom'designated generally as 92 is illustrated; In responseto anelectrical signal from theload cells 36 and;38, the controller 44aotuates' the alarm 54 and transmits'a signal to the controller72, 1 Thecontroller 72,-inturn, actuates the solenoid 34 thereby closingthe'valve 32. When'the valve 32- is closed,

the heat exchanger 22 ceases to be eifective- 7 Another. embodiment ofthe present invention designated generallyas 93 is illustrated in FIGURE5. In

orderto ascertain the change in the weight of the articles 62- which arebeing freeze dried, an electrical resistor 74 is'dispos'ed within one ormore ofthearticles' 62. The

resistor 72 is disposed ina11 electrical'circuit having a source0f=power .76j'with the ehange in resistance being fed to thecontroller44 through an amplifieri78,

As the ice inthe articles 62 sublimesgjthe 'resista nce of the articles.62 is constantly changing. WhenHsubstari- ,tially .all of the ice hass'ublimed fromthe articles'62, the V resistance through the articles 62will be substantially .35 tion of ice from the articles.

.59 V 4. A method of treating artlc signal; V r r g 1 5.- A rnethod inlaccordance with claim 4 wherein said varying} step includes controllingthe pressure'in said en- 60 closure in response to said'signal.

constant At'this point; the controller 44 will activate the alarm'54 andtransmit a-signal to the controller 72 which causes the solenoid 34 toclose the valve 32.

Then, it will betseen that the present invention disthe freeze dryingprocess in response'to the change of Weight of the articles beingfreezedried. It will be apr preciated by those skilled in the art thatit may be desirable to? combine orieor more of the embodimentsillusvalve 32 at the same timethat the valve 63 is closed.

The present invention may be embodied in other specific formslwithoutdeparting from the spirit or essential attributes thereof and,accordingly, reference should be i made to the appendedclaimg'ratherthan to the foregoing g0 specification as indicating the scope of theinvention.

I claim; 7 v 5 1.. Apparatus for freeze dryingarticles of substantiallyI the same size andkind comprisinga housing having a chamber therein, a.shelf within said chamber, a tray for 2 5" frozen: articles tobe-freeze dried within said housing, said tray being supported on saidshelf, means forfreeze drying the articles on said tray by causing icein the frozen specimens to sublime, and means responsive to the loss ofweight of the articles for automaticallycontrolling said freeze dr inmeans, said last-mentionedmeans including at least one load cellsupporting the Weight of said tray f and the articles to be freezedried, whereby an electrical signal maybeg'enerat'ed which varies inaccordance with the change of weight of the 'articles'due' to thesublima- 2. Apparatus in accordance withclaim lrwhereinfsaid 7 freezedrying means includesa valved -conduit through which the pressure 'insaid'chamber'can be controlled, and the valve of saidvalved conduitbeing coupled to said 3. A method of freezedrying 'ar'ticles ofsubstantially thes amesiz e and kind comprising the steps of freezingarticle s, disposing said frozenarticles in a hermetically,sealedpnclosurje,evacuating said enclosure while subjecting said"articlesto heat so as to'cjause ice in said frozen 'L articlestosublime, and automatically continuously weighing the articles andgenerating asignalas a function there- 1 of, and controlling the amountof heat supplied to said articles inrepsonse to said signal. r

7 les of substantially the samefsize and kind comprising freezedryingf'said-articles fin, a "he'rmetically sealed enclosure,automatically-icontinuously weighing the articles to ascertain thechange in "loss-of Weight of the articles du'e'to sublimation of icetherefrom and generating a signalas a function thereof,

, and varying saidffreeze drying process in response to'said 6. A methodinaccordance withclaim 4 wherein said weighing step includes supportingthe articles by load cells,

and saidstep of generating a signal being accomplished by theload cellsso thatthe signal generated will vary in accordance with the changeofweight of the articles due to the sublimation of ice from the articles;r

7.. Apparatus for freeze fdry'ng articles of substantially; thesame sizeand kind comprising a housing having a chambe'r'therein, a'shelf'withinsaid chamber, said shelf being adapted to support frozen articles tobefre'eze dried within s aidhousing means for freeze drying the articlesI I on; said shelf byeausing ice in the frozen'articles', to sublime,and' wei'ghingfmeansfdirectlyjresponsive to the; loss f of weight jofthearticles for automatically controlling '75, saidfreezedrying-means; e rI 8. Apparatus in accordance with claim 7 wherein said means responsiveto the loss of weight includes a device for varying the pressure in saidchamber.

9. Apparatus in accordance with claim 8 wherein said device is a valvedconduit for introducing a gas into the chamber.

10. Apparatus in accordance with claim 8 wherein said device is a valvedconduit through which the chamber may be evacuated.

References Cited by the Examiner UNITED STATES PATENTS 2,994,132 8/61Neumann 34-5 3,020,645 2/62 Copson 34-5 3,060,591 10/62 Lieberman 34-453,077,036 2/63 Neurnann 34--5 3,078,586 2/63 Rey 34-5 NORMAN YUDKOFF,Primary Examiner.

1. APPARATUS FOR FREEZE DRYING ARTICLES OF SUBSTANTIALLY THE SAME SIZEAND KIND COMPRISING A HOUSING HAVING A CHAMBER THEREIN, A SHELF WITHINSAID CHAMBER, A TRAY FOR FROZEN ARTICLES TO BE FREEZE DRIED WITHIN SAIDHOUSING, SAID TRAY BEING SUPPORTED ON SAID SHELF, MEANS FOR FREEZEDRYING THE ARTICLES IN SAID TRAY BY CAUSING ICE IN THE FROZEN SPECIMENSTO SUBLIME, AND MEANS RESPONSIVE TO THE LOSS OF WEIGHT OF THE ARTICLESFOR AUTOMATICALLY CONTROLLING SAID FREEZE DRYING MEANS, SAIDLAST-MENTIONED MEANS INCLUDING AT LEAST ONE LOAD CELL SUPPORTING THEWEIGHT OF SAID TRAY AND THE ARTICLES TO BE FREEZE DRIED, WHEREBY ANELECTRICAL SIGNAL MAY BE GENERATED WHICH VARIES IN ACCORDANCE WITH THECHANGE OF WEIGHT OF THE ARTICLES DUE TO THE SUBLIMATION OF ICE FROM THEARTICLES.